KR102574672B1 - Workpiece processing method - Google Patents

Abstract

An object of the present invention is to provide a method for processing a workpiece in which adhesion of abrasive grains to device chips is prevented.
As a method for processing a workpiece, a laser beam L having a wavelength that is transparent to a workpiece 11 is irradiated from the back surface 11b side of the workpiece along a line 13 to be divided, and a device chip 19 After carrying out the modified layer formation step of forming the modified layer 17 on the back side from a position corresponding to the finished thickness of , and the modified layer forming step, the back surface of the workpiece is ground to process the workpiece to the finished thickness of the device chip After carrying out the back grinding step of performing, the modified layer formation step, and the dividing step of dividing the workpiece into individual device chips along the division line on which the modified layer is formed, the back side grinding step and the dividing step, including abrasive grains and a polishing step of removing grinding strain on the back surface of the workpiece by polishing the backside of the workpiece using a polishing pad 44 containing abrasive grains while supplying a polishing liquid that is not applied to the workpiece.

Description

Processing method of work piece {WORKPIECE PROCESSING METHOD}

The present invention relates to a method for processing a workpiece in which a plate-shaped workpiece is divided into a plurality of device chips.

BACKGROUND OF THE INVENTION In electronic devices typified by mobile phones and personal computers, device chips including electronic circuits (devices) have become essential components. A device chip is formed by dividing the surface of a wafer made of a semiconductor material such as silicon by a plurality of scheduled division lines (streets), forming electronic circuits in each region, and then dividing the wafer along these scheduled division lines. are manufactured

As one of the methods of dividing a wafer, penetrating laser beams are condensed inside the wafer to form a modified region (modified layer) by multiphoton absorption, and the wafer is divided into device chips using this modified region as a starting point for division. Stealth dicing (SD) is known (see, for example, Patent Document 1).

In stealth dicing, since it is not necessary to form grooves in the wafer by cutting or the like, the number of device chips taken can be increased by reducing the width of the line to be divided. On the other hand, this stealth dicing has a problem that the transverse strength of the device chip tends to decrease due to the remaining modified regions.

In order to solve this problem, after forming a modified region from the back side of the wafer to a position at a depth that does not reach the finished thickness of the device chip, SDBG divides the wafer into device chips while removing the modified region by grinding the back side of the wafer. (Stealth Dicing Before Grinding) is under review (see, for example, Patent Literature 2 and Patent Literature 3).

However, when the wafer is ground, grinding deformation occurs on the back surface, which is the surface to be ground, and the bending strength of the device chip is lowered. Therefore, after grinding the wafer, the grinding strain is removed by polishing the wafer by a method such as CMP (Chemical Mechanical Polishing).

Japanese Unexamined Patent Publication No. 2002-192370 International Publication No. 2003/77295 Japanese Unexamined Patent Publication No. 2006-12902

However, when the wafers ground and divided by the SDBG described above are polished by CMP, the free abrasive grains contained in the polishing liquid invade gaps between adjacent device chips and adhere to the side surfaces. When abrasive grains adhere to the side surfaces of the device chips, problems tend to occur in subsequent processes.

The present invention has been made in view of these problems, and its object is to provide a method for processing a workpiece in which adhesion of abrasive grains to device chips is prevented.

According to the present invention, a method for processing a workpiece in which a plate-shaped workpiece is divided into a plurality of device chips along a line along which a plate-shaped workpiece is to be divided is provided by emitting a laser beam having a wavelength that is transparent to the workpiece from the back side of the workpiece. A modified layer forming step of irradiating along a line to be divided and forming a modified layer on the back side from a position corresponding to the finished thickness of the device chip, and grinding the back surface of the workpiece after performing the modified layer forming step Dividing the workpiece into individual device chips along the planned division line on which the modified layer is formed after performing the backside grinding step of processing the workpiece to the finished thickness of the device chip and the modified layer forming step by performing After performing the dividing step, the back surface grinding step, and the dividing step, the back surface of the workpiece is polished using a polishing pad containing abrasive grains while supplying a polishing liquid containing no abrasive grains to the workpiece, A method for processing a workpiece is provided, comprising a polishing step of removing grinding deformation of the back surface of the workpiece.

In the present invention, it is preferable to further include a gettering layer forming step of forming a gettering layer on the back surface of the workpiece after performing the polishing step.

In the present invention, the hardness (Asker-C) of the polishing pad is 55 degrees to 90 degrees, the compression ratio of the polishing pad is 2% to 15%, and the material of the abrasive grain included in the polishing pad is, Diamond, green carborundum, white alundum, ceria or zirconia, and the abrasive grain included in the polishing pad preferably has a particle diameter of 0.01 μm to 10 μm.

Further, in the present invention, it is preferable that the polishing liquid is an alkaline solution.

In the method for processing a workpiece according to the present invention, in the polishing step, the workpiece is polished using a polishing pad containing abrasive grains while supplying a polishing liquid not containing abrasive grains to the workpiece. Unlike the conventional method using liquid, abrasive grains do not adhere to the side surfaces of the device chips.

1 is a perspective view schematically showing a workpiece or the like.
2 is a perspective view schematically illustrating a modified layer forming process.
3(A) and 3(B) are partial cross-sectional side views schematically showing the backside grinding step and the dividing step.
Fig. 4(A) is a partial cross-sectional side view schematically showing the polishing step, and Fig. 4(B) is a cross-sectional view schematically showing the workpiece after the polishing step.

EMBODIMENT OF THE INVENTION With reference to accompanying drawings, embodiment of this invention is described. The method for processing a workpiece according to the present embodiment includes a modified layer forming step (see Fig. 2), a back surface grinding step (see Fig. 3(A) and Fig. 3(B)), a dividing step (see Fig. 3(A) ) and FIG. 3 (B)), a polishing process (see FIG. 4 (A) and FIG. 4 (B)), and a gettering layer forming process.

In the modified layer forming step, a laser beam having a wavelength having transparency is irradiated to the workpiece to form a modified layer along the line to be divided. In the backside grinding step, the backside of the workpiece is ground to process the workpiece to the finished thickness of the device chip. In the dividing step, the workpiece is divided into device chips along the dividing line.

In the polishing step, the back surface of the workpiece is polished using a polishing pad containing abrasive grains while supplying polishing liquid containing no abrasive grains to the workpiece. As a result, grinding strain on the back side of the workpiece is eliminated. In the gettering layer formation step, a gettering layer is formed on the back surface of the workpiece. Hereinafter, the processing method of the workpiece according to the present embodiment will be described in detail.

1 is a perspective view schematically showing a workpiece or the like processed in the present embodiment. As shown in FIG. 1, the workpiece 11 is a disc-shaped wafer made of, for example, a semiconductor material such as silicon, and the surface 11a side thereof has a central device region and an outer circumferential excess surrounding the device region. divided into areas. The device area is further partitioned into a plurality of areas by a plurality of lines to be divided (streets) 13 arranged in a grid, and devices 15 such as ICs and LSIs are formed in each area.

Further, in this embodiment, a wafer made of a semiconductor material such as silicon is used as the workpiece 11, but the material, shape, and the like of the workpiece 11 are not limited. For example, a substrate made of a material such as ceramic, resin, or metal may be used as the workpiece 11 . Similarly, there are no restrictions on the arrangement of the line to be divided 13 or the type of device 15.

In the dividing method of the workpiece according to the present embodiment, first, the protection member 21 is attached to the surface 11a side of the workpiece 11 . The protection member 21 is, for example, an adhesive tape having substantially the same shape as the workpiece 11, a resin substrate, a wafer of the same or different type as the workpiece 11, and an adhesive or the like on the first surface 21a side thereof. An adhesive layer consisting of is formed.

Therefore, the protection member 21 can be adhered to the workpiece 11 by bringing the first surface 21a side of the protection member 21 into contact with the front surface 11a side of the workpiece 11 . By attaching the protection member 21 to the workpiece 11 in this way, it is possible to prevent damage to the device 15 due to a load applied during grinding.

After attaching the protection member 21 to the workpiece 11, a modified layer forming step of irradiating the workpiece 11 with a laser beam having a wavelength having transparency to form a modified layer along the line to be divided is performed. do. 2 is a perspective view schematically illustrating a modified layer forming process. The modified layer formation process is performed by, for example, the laser processing apparatus 2 shown in FIG. 2 .

The laser processing device 2 includes a chuck table 4 that sucks and holds the workpiece 11 . The chuck table 4 is connected to a rotation drive source (not shown) such as a motor, and rotates around a rotation axis substantially parallel in the vertical direction. Further, a table moving mechanism (not shown) is provided below the chuck table 4, and the chuck table 4 is moved horizontally by this table moving mechanism.

The upper surface of the chuck table 4 serves as a holding surface for sucking and holding the second surface 21b side of the protection member 21 adhered to the workpiece 11 . A negative pressure from a suction source (not shown) acts on this holding surface via a flow path (not shown) formed inside the chuck table 4 or the like, and a suction force for sucking the protective member 21 is generated.

Above the chuck table 4, a laser processing unit 6 is disposed. At a position adjacent to the laser processing unit 6, a camera 8 for capturing an image of the workpiece 11 is installed. The laser processing unit 6 downwardly irradiates the laser beam L pulse-oscillated by a laser oscillator (not shown). The laser oscillator is configured to pulse oscillate the laser beam L of a wavelength that is difficult to be absorbed by the workpiece 11 (a wavelength having transparency).

In the modified layer forming step, first, the second surface 21b of the protection member 21 adhered to the workpiece 11 is brought into contact with the holding surface of the chuck table 4, and negative pressure from the suction source is applied. In this way, the workpiece 11 is attracted and held by the chuck table 4 in a state where the back surface 11b side is exposed upward.

Next, the chuck table 4 holding the workpiece 11 is moved and rotated to align the laser processing unit 6 with the end of the line 15 to be divided to be processed. Then, while irradiating the laser beam L from the laser processing unit 6 toward the back surface 11b of the workpiece 11, the chuck table 4 is moved in a direction parallel to the division line 13 of the object to be processed. move to That is, the laser beam L is irradiated from the back surface 11b side of the workpiece 11 along the line to be divided 13 .

At this time, the position of the converging point of the laser beam L is inside the workpiece 11 and is aligned with the back surface 11b side from a position corresponding to the finished thickness of the device chip. Accordingly, the vicinity of the convergence point of the laser beam L is modified by multiphoton absorption, and the modified layer 17 along the line 15 to be divided to be processed can be formed. That is, the modified layer 17 is formed on the back surface 11b side from a position corresponding to the finished thickness of the device chip. When the modified layer 17 is formed along all of the lines 15 to be divided, the process of forming the modified layer is finished.

After the modified layer forming step, a back surface grinding step of grinding the back surface 11b of the workpiece 11 and a dividing step of dividing the workpiece 11 into device chips are performed. 3(A) and 3(B) are partial cross-sectional side views schematically showing the backside grinding step and the dividing step. The back surface grinding process and the dividing process are performed by the grinding device 12 shown in FIG. 3(A) and FIG. 3(B), for example.

The grinding device 12 includes a chuck table 14 that sucks and holds the workpiece 11 . The chuck table 14 is connected to a rotation drive source (not shown) such as a motor, and rotates around a rotation axis substantially parallel in the vertical direction. Further, a table moving mechanism (not shown) is provided below the chuck table 14, and the chuck table 14 is moved horizontally by this table moving mechanism.

The upper surface of the chuck table 14 serves as a holding surface 14a for sucking and holding the second surface 21b side of the protection member 21 adhered to the workpiece 11 . A negative pressure from a suction source (not shown) acts on the holding surface 14a via a flow path (not shown) or the like formed inside the chuck table 14, and a suction force for sucking the protective member 21 is generated. Occurs.

Above the chuck table 14, a grinding unit 16 is disposed. The grinding unit 16 has a spindle housing 18 supported by a grinding unit elevating mechanism (not shown). A spindle 20 is accommodated in the spindle housing 18, and a disc-shaped mount 22 is fixed to the lower end of the spindle 20.

On the lower surface of the mount 22, a grinding wheel 24 having approximately the same diameter as the mount 22 is mounted. The grinding wheel 24 has a wheel base 26 made of a metal material such as stainless steel or aluminum. On the lower surface of the wheel base 26, a plurality of grinding stones 28 are arranged in an annular shape.

A rotation drive source (not shown) such as a motor is connected to the upper end side (base end side) of the spindle 20 . The grinding wheel 24 is rotated around a rotational axis substantially parallel in the vertical direction by rotational force transmitted from this rotational drive source.

In the backside grinding process and the dividing process, first, the second surface 21b of the protection member 21 adhered to the workpiece 11 is brought into contact with the holding surface 14a of the chuck table 14, and negative pressure from the suction source is applied. act on In this way, the workpiece 11 is attracted and held by the chuck table 14 in a state where the back surface 11b side is exposed upward.

Next, the chuck table 14 is moved downward of the grinding wheel 24. Then, as shown in (A) of FIG. 3, the chuck table 14 and the grinding wheel 24 are rotated to lower the spindle housing 18 while supplying a grinding liquid such as deionized water. The descending amount of the spindle housing 18 is adjusted to such an extent that the lower surface of the grinding wheel 28 is pressed against the lower surface 11b of the workpiece 11 .

Thereby, the back surface 11b side of the workpiece 11 can be ground. This grinding is performed while measuring the thickness of the to-be-processed object 11, for example. In this embodiment, since the modified layer 17 is formed along the line 13 to be divided, the workpiece 11 is broken starting from the modified layer 17 by the pressure applied during grinding, and divided It is divided along the planned line.

As shown in FIG. 3(B), when the workpiece 11 is thinned to the finished thickness and divided into a plurality of device chips 19 along all the division lines 13, the back side grinding process and the division process is terminated.

In addition, in this embodiment, since the modified layer 17 is formed on the back surface 11b side from a position corresponding to the finished thickness of the device chip 19, the workpiece 11 is thinned to the finished thickness of the device chip. If so, the modified layer 17 is completely removed from the workpiece 11 . Therefore, the bending strength of the device chip 19 does not decrease due to the remaining modified layer 17 .

After the dividing step, a polishing step of polishing the back surface 11b of the workpiece 11 is performed. Fig. 4(A) is a partial cross-sectional side view schematically illustrating the polishing step. The polishing process is performed by, for example, the polishing device 32 shown in FIG. 4(A). The polishing device 32 includes a chuck table 34 that sucks and holds the workpiece 11 .

The chuck table 34 is connected to a rotation drive source (not shown) such as a motor, and rotates around a rotation axis substantially parallel in the vertical direction. Further, below the chuck table 34, a table moving mechanism (not shown) is provided, and the chuck table 34 is moved horizontally by this table moving mechanism.

The upper surface of the chuck table 34 serves as a holding surface 34a for sucking and holding the second surface 21b side of the protection member 21 adhered to the workpiece 11 . A negative pressure from a suction source (not shown) acts on the holding surface 34a via a flow path (not shown) or the like formed inside the chuck table 34, and a suction force for sucking the protective member 21 is generated. Occurs.

Above the chuck table 34, a polishing unit 36 is disposed. The polishing unit 36 includes a spindle housing 38 supported by a polishing unit elevating mechanism (not shown). The spindle 40 is accommodated in the spindle housing 38, and a disc-shaped mount 42 is fixed to the lower end of the spindle 40.

On the lower surface of the mount 42, a polishing pad 44 having approximately the same diameter as the mount 42 is mounted. This polishing pad 44 is composed of, for example, a polishing cloth made of nonwoven fabric, foamed urethane, or the like, and abrasive grains fixed to the polishing cloth. The thickness of the polishing pad 44 is, for example, 3 mm or more, and grooves with a depth of 2.5 mm or more are formed in a lattice shape on the entire lower surface (polishing surface) of the polishing pad 44 .

The hardness (Asker-C) of the polishing pad 44 is preferably 55 to 90 degrees, and the compressibility of the polishing pad 44 is preferably 2% to 15%. In addition, the compression rate is determined by taking the thickness of the polishing pad 44 when a load of 300 g/cm 2 is applied as t1 and the thickness of the polishing pad 44 when a load of 2000 g/cm 2 is applied as t2, (t1- t2)/t1×100. By setting the compression ratio of the polishing pad 44 to 2% to 15%, chipping of the edge of the workpiece 11 can be suppressed while maintaining a high polishing rate.

In addition, the material of the abrasive grain is, for example, diamond, green carborundum, white alundum, ceria, zirconia, etc., and the particle diameter of the abrasive grain is, for example, 0.01 µm to 10 µm, preferably 0.1 µm to 2 µm. However, the material of the abrasive grain and the grain size of the grain can be arbitrarily changed depending on the material of the workpiece 11 and the like.

A rotation drive source (not shown) such as a motor is connected to the upper end side (base end side) of the spindle 40 . The polishing pad 44 is rotated around a rotational axis substantially parallel in the vertical direction by rotational force transmitted from the rotational driving source.

When polishing the back surface 11b of the workpiece 11, first, the second surface 21b of the protection member 21 adhered to the workpiece 11 is placed on the holding surface 34a of the chuck table 34. By contacting it, the negative pressure of the suction source is applied. In this way, the workpiece 11 is attracted and held by the chuck table 34 in a state where the back surface 11b side is exposed upward.

Next, the chuck table 34 is moved downward of the polishing pad 44 . Then, as shown in FIG. 4(A), the chuck table 34 and the polishing pad 44 are rotated to lower the spindle housing 38 while supplying the polishing liquid. The descending amount of the spindle housing 38 is adjusted to such an extent that the lower surface (polishing surface) of the polishing pad 44 is pressed against the lower surface 11b of the workpiece 11 . In this way, grinding deformation can be removed by polishing the back surface 11b of the workpiece 11 .

As the polishing liquid, for example, an alkali solution containing no abrasive grains is used. This is because if the abrasive grains are included in the polishing liquid, the abrasive grains tend to remain in the gaps between adjacent device chips 19 . In the present embodiment, since the polishing pad 44 containing abrasive grains is used, the workpiece 11 can be appropriately polished without including the abrasive grains in the polishing liquid. Moreover, as an alkali solution, potassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide (TMAH), potassium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, etc. can be used.

Fig. 4(B) is a cross-sectional view schematically showing the workpiece 11 after the polishing step. In the polishing step of the present embodiment, as described above, since the workpiece 11 is polished using a polishing liquid that does not contain abrasive grains, the abrasive grains adhere to the side surfaces of the device chips 19 corresponding to the dividing grooves. There is no work.

After the polishing step, a gettering layer forming step of forming a gettering layer on the back surface of the workpiece 11 is performed. The gettering layer forming step is performed in the same manner as the polishing step, for example, using the polishing device 32 used in the polishing step. However, in this gettering layer forming step, the lower surface (polishing surface) of the polishing pad 44 is brought into contact with the lower surface 11b of the workpiece 11 without being pressed against it. That is, no pressure is applied to the workpiece 11 from the polishing pad 44 .

In this way, by slightly rubbing the back surface 11b of the workpiece 11 with the polishing pad 44, a gettering layer including fine strain is formed. By this gettering layer, contamination of the device 15 by a metal element or the like can be prevented. Moreover, it is also possible to make a gettering layer by making some grinding strain formed in the back side grinding process remain. In this case, it is not necessary to perform the gettering layer forming process after the polishing process.

As described above, in the method for processing a workpiece according to the present embodiment, in the polishing step, while supplying the polishing liquid containing no abrasive grains to the workpiece 11, the polishing pad 44 containing abrasive grains is used to Since the workpiece 11 is polished, the abrasive grains do not adhere to the side surfaces of the device chips 19 unlike conventional methods using a polishing liquid containing abrasive grains.

In addition, this invention is not limited to the description of the said embodiment, and can be implemented with various changes. For example, in the above embodiment, the back surface grinding process and the dividing process are performed simultaneously, but the back surface grinding process and the dividing process may be separately performed.

Specifically, for example, after performing the dividing step, the backside grinding step can be performed. In this case, for the dividing step, for example, a method of expanding an expandable tape adhered to the workpiece 11, a method of pressing the workpiece 11 along the line 13 along which the workpiece 11 is to be divided, and the like can be employed. .

Of course, after performing the backside grinding process and the dividing process according to the above embodiment, if necessary, a dividing process of expanding the expand tape or a dividing process of pressing with a pressing blade may be additionally performed.

In addition, the structure, method, etc. according to the above embodiment can be appropriately changed and implemented without departing from the scope of the purpose of the present invention.

11: Workpiece 11a: Surface
11b: back side 13: line to be divided (street)
15: device 17: modified layer
19: device chip 21: protection member
21a: first surface 21b: second surface
L: laser beam 2: laser processing device
4: chuck table 6: laser processing unit
8: camera 12: grinding device
14: chuck table 14a: holding surface
16: grinding unit 18: spindle housing
20: spindle 22: mount
24: grinding wheel 26: wheel base
28: grinding grindstone 32: polishing device
34: chuck table 34a: holding surface
36: polishing unit 38: spindle housing
40: spindle 42: mount
44: polishing pad

Claims (3)

A method for processing a workpiece in which a plate-shaped workpiece is divided into a plurality of device chips along a division line, comprising:
A modified layer for irradiating a laser beam having a wavelength that is transparent to the workpiece from the back side of the workpiece along the line to be divided, and forming a modified layer on the backside side from a position corresponding to the finished thickness of the device chip. forming process;
After performing the modified layer forming step, a back surface grinding step of grinding the back surface of the workpiece to process the workpiece to a finished thickness of the device chip;
a dividing step of dividing the workpiece into individual device chips along the planned division line on which the modified layer is formed after performing the modified layer forming step;
After the back surface grinding step and the dividing step are performed, the back surface of the workpiece is polished using a polishing pad containing abrasive grains while supplying a polishing liquid containing no abrasive grains to the workpiece, A polishing process to remove grinding deformation;
A gettering layer forming step of forming a gettering layer on the back surface of the workpiece after performing the polishing step
including,
In the gettering layer forming step, the gettering layer is formed by bringing the polishing pad into contact with the back surface of the workpiece in a state in which no pressure is applied without pressing the polishing pad. The method of claim 1, wherein the polishing pad has a hardness (Asker-C) of 55 to 90 degrees,
The compression rate of the polishing pad is 2% to 15%,
The material of the abrasive grain included in the polishing pad is diamond, green carborundum, white alundum, ceria or zirconia,
The method of processing a workpiece, characterized in that the grain size of the abrasive grain contained in the polishing pad is 0.01 μm to 10 μm. The method for processing a workpiece according to claim 1 or 2, wherein the polishing liquid is an alkaline solution.